Various wireless access technologies have been proposed or implemented to enable mobile stations to perform communications with other mobile stations or with wired terminals coupled to wired networks. Examples of wireless access technologies include GSM (Global System for Mobile communications) and UMTS (Universal Mobile Telecommunications System) technologies, defined by the Third Generation Partnership Project (3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies, defined by 3GPP2.
As part of the continuing evolution of wireless access technologies to improve spectral efficiency, to improve services, to lower costs, and so forth, new standards have been proposed. One such new standard is the Long Term Evolution (LTE) standard from 3GPP, which seeks to enhance the UMTS wireless network. The CDMA 2000 wireless access technology from 3GPP2 is also evolving. The evolution of CDMA 2000 is referred to as the Ultra Mobile Broadband (UMB) access technology, which supports significantly higher rates and reduced latencies.
Another type of wireless access technology is the WiMAX (Worldwide Interoperability for Microwave Access) technology. WiMAX is based on the IEEE (Institute of Electrical and Electronics Engineers) 802.16 Standard. The WiMAX wireless access technology is designed to provide wireless broadband access.
A few variations of hybrid automatic repeat request (HARQ) transmission/operation schemes exist in the above identified access technologies. One variation is unicast HARQ in which each encoded packet includes data from one user. This can be fully asynchronous in which case the modulation and coding scheme (MCS), transmission time (slot/frame) and resource allocation are independent for each transmission of an encoded packet (first and all re-transmissions). Assignment signaling is used to describe the resource allocation, MCS and user IDs for each transmission and re-transmission. While this approach allows adaptation to real time channel conditions, it incurs large signaling overhead. Unicast HARQ can alternatively be fully synchronous. In this case, the MCS scheme for transmissions (first and all retransmissions) is the same, resource allocation (location) remains the same for first and all retransmissions (the transmission location must be the same as the first transmission). The transmission interval is fixed, and assignment signaling is required only for the first transmission. This enables lower signaling overhead for retransmission, but can cause significant scheduling complexity and signaling overhead for the first transmission due to the irregular vacancies of resources that occurs since some resources need to be reserved for retransmissions that may not be necessary.
Another HARQ variant is multicast HARQ in which each encoded packet includes data for multiple users. The worst channel quality indicators (CQIs) among multiple users are considered for selecting MCS. The entire packet is retransmitted if one or more users could not decode it successfully, even though some of the users may have successfully decoded the packet. Multi-cast HARQ can be implemented using fully asynchronous and fully synchronous schemes.